The Wicklow Mountains (Irish: Sléibhte Chill Mhantáin,[1]archaic: Cualu) form the largest continuous upland area in Ireland. They occupy the whole centre of County Wicklow and stretch outside its borders into Counties Carlow, Wexford and Dublin. Where the mountains extend into County Dublin, they are known locally as the Dublin Mountains (Irish: Sléibhte Bhaile Átha Cliath).[1] The highest peak is Lugnaquilla at 925 metres (3,035 feet).

The mountains are primarily composed of granite surrounded by an envelope of mica-schist and much older rocks such as quartzite. They were pushed up during the Caledonian orogeny at the start of the Devonian period and form part of the Leinster Chain, the largest continuous area of granite in Ireland and Britain. The mountains owe much of their present topography to the effects of the last ice age, which deepened the valleys and created corrie and ribbon lakes. Copper and lead have been the main metals mined in the mountains and a brief gold rush occurred in the 18th century.

The mountains have been inhabited since Neolithic times and a number of typical monuments, in particular a series of passage tombs, survive to the present day. The monastery at Glendalough, founded in the late 6th century by Saint Kevin, was an important centre of the Early Church in Ireland. Following the Norman invasion in the 12th century, the Wicklow Mountains became a stronghold and hiding place for Irish clans opposed to English rule. The O'Byrne and O'Toole families carried out a campaign of harassment against the settlers for almost five centuries. Later the mountains harboured rebels during the 1798 Rising. Rebel activity died out after the construction of the Wicklow Military Road at the start of the 19th century and the mountains began to attract tourists to the ruins at Glendalough and to admire the mountain scenery.

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The Wicklow Mountains take their name from County Wicklow which in turn takes its name from Wicklow town. The origin of the name is from the DanishWykynglo or Wykinlo.[2] The Irish name for Wicklow, Cill Mhantáin, means "Church of Mantan", named after an apostle of Saint Patrick.[2] Wicklow was not established as a county until 1606; prior to that it had been part of County Dublin.[3] An early name for the whole area of the Wicklow Mountains was Cualu.[4] There are also historic names for various territories in the mountains held by local clans: the north part of Wicklow and south Dublin was known as Cualann while the Glen of Imaal takes its name from the territory of Hy Mail.[2] A sept of the O'Byrne family called the Gaval Rannall possessed the area around Glenmalure, known as Gaval-Rannall or Ranelagh.[2] During the medieval period, prior to the establishment of County Wicklow, the English administration in Dublin referred to the region as the Leinster Mountains.[5]

Lugnaquilla is the highest peak in the Wicklow Mountains at 925 metres (3,035 feet) and the 13th highest in Ireland.[9] It is also the highest peak in Leinster and is the only Irish Munro to be found outside of Munster.[10]Kippure, at 757 metres (2,484 feet), is the highest mountain in County Dublin.[11] There are a total of 39 peaks over 600 metres (2,000 feet) in the Wicklow Mountains.[12] There are only three passes through the mountains under 600 metres (2,000 feet) with the Sally Gap (498 metres (1,634 feet)) and the Wicklow Gap (478 metres (1,567 feet)) being the highest road passes in the country.[13]

Iapetus closed up completely at the end of the Silurian period (443-415 million years ago) and the Wicklow Mountains were uplifted during the main phase of the Caledonian orogeny at the start of the Devonian period (415-358 million years ago) when the continents of Baltica and Laurentiacollided.[18] The collision pushed up a large batholith of granite, known as the Leinster Chain: this is the largest continuous area of granite in Ireland and Britain and runs from the coast at Dun Laoghaire in County Dublin to New Ross in County Wexford and includes the Wicklow and Blackstairs Mountains.[19][20] The heat generated by the collision metamorphosed the slates and shales surrounding the granite into schists which formed an aureole (shell) around the granite.[21] The process of erosion has removed much of the surrounding schist from the mountain tops, exposing the underlying granite.[22] Some remnants of the schist roof remain on some of the mountain tops, most notably Lugnaquilla.[21] The round granite topped peaks contrast with the sharper schist peaks: for example, War Hill (granite) and Djouce (schist).[23]

The zone of collision between the continental plates that led to the formation of the Wicklow Mountains also led to mineralisation and the formation of Ireland's most significant metalliferous belt.[28] The most important mining sites have been at Avoca and Glendalough. Mining has taken place at Avoca since at least the Bronze Age (c. 2,500–600 BCE).[29] Iron ore extraction took place between the 12th and 17th centuries before being replaced by lead mining up to the mid 18th century.[30] The principal activity from 1720 to the closure of the last mine in 1982 was copper extraction.[31]Sulphur has also been extracted at certain times and, in smaller quantities, gold, silver and zinc.[32] Lead mining has been the principal activity in the Glendalough valley and its neighbouring valleys of Glendasan and Glenmalure. Lead was first discovered in Glendasan in the early 19th century and the lead veins were later followed through Camaderry mountain to Glendalough.[33] Mining on a smaller scale took place in Glenmalure.[34] Ore from these mines was shipped to Ballycorus for processing.[35] The last mine closed in 1957.[36]

In 1795, a local schoolmaster discovered gold in the Aughatinavought River, a tributary of the River Aughrim since renamed Gold Mines River that rises on the slopes of Croghan Kinsella mountain.[37] During the subsequent gold rush, some 80 kilograms (180 pounds) of gold was recovered from the river by local prospectors, including a single nugget weighing 682 grams (24.1 ounces), the largest lump of gold ever discovered in Ireland and Britain.[37] The mine workings were subsequently seized by the British government who extracted a further 300 kilograms (660 pounds) of gold.[37] Various attempts have been made to locate the motherlode on Croghan Kinsella but to no avail.[37]

The Wicklow Mountains are the source of several major river systems. Since the thin blanket bogpeats cannot hold great quantities of water, many of these rivers exhibit a flashy hydrography, filling rapidly after heavy rain.[41]

The River Vartry rises on the slopes of Djouce mountain.[2] Nearby, the River Dargle rises between Tonduff and War Hill, falling as the Powerscourt Waterfall, Ireland's tallest waterfall at 121 metres (397 feet),[44] over a cliff formed by a glacier at the contact point between the granite and mica-schist of the Wicklow Mountains.[45] The waterfalls at the heads of the valleys of Glendalough, Glenmacnass and Glendasan also occur approximately at the schist-granite junctions,[46] as does the Carrawaystick waterfall in Glenmalure.[47]

The River Slaney rises in the North Prison of Lugnaquilla mountain and winds through the Glen of Imaal where it is joined by the Leoh, Knickeen and Little Slaney.[48] Another of its tributaries, the River Derreen, rises on Lugnaquilla's southern side.[49]

Each of the main branches of the River Avoca – the Avonmore, the Avonbeg and the Aughrim rivers – have their origins in smaller tributaries, many of which rise in the Wicklow Mountains.[2] The Glenealo, Glendasan and Annamoe rivers meet to form the Avonmore near Laragh.[2] The Annamoe rises near Sally Gap and is joined by Cloghoge Brook between Lough Tay and Lough Dan and by the River Inchavore in Lough Dan.[2] The Avonbeg rises on Table Mountain and the Three Lakes.[2] The Avonmore and Avonbeg rivers join to form the River Avoca at the Meeting of the Waters in the Vale of Avoca, celebrated in the song The Meeting of the Waters by Thomas Moore.[41] The Avoca is joined by the River Aughrim at Woodenbridge, sometimes referred to as the "Second Meeting of the Waters".[2] The Aughrim is formed at the junction of the Derry Water and the River Ow, the latter of which rises on Lugnaquilla.[2]

Several of these rivers have been dammed to create reservoirs to provide drinking water for the residents of Dublin and its environs. The first of these was the River Vartry, dammed to create the Vartry Reservoir near Roundwood in the 1860s.[50] A second dam was added in 1924 to increase capacity.[50] The River Dodder feeds the two Bohernabreena reservoirs in the northern foothills of the Wicklow Mountains at Glenasmole in County Dublin, which were constructed between 1883 and 1887 to supply water to the townland of Rathmines.[51] The Poulaphouca Reservoir, on the River Liffey near Blessington, was constructed between 1938 and 1940.[52] There are also two hydroelectricity plants at Poulaphouca, constructed during the 1940s.[53] A pumped storage hydroelectricity plant was constructed at Turlough Hill between 1968 and 1974.[54] Water is pumped up from Lough Nanahangan, a natural corrie lake, into an artificial reservoir on Tomaneena mountain and released at times of peak electricity demand.[55][56]

In common with the rest of Ireland, the Wicklow Mountains experience a temperateoceanic climate with mild, damp summers and cool, wet winters.[57] Annual rainfall reaches 2,000 mm (79 inches) on the highest mountains with the more westerly peaks getting the most rainfall (for example, Djouce mountain, in the east, receives c. 1,630 mm (64 inches) whereas Duff Hill, in the west, receives c. 1,950 mm (77 inches) a year).[58] June and July are generally the driest months and there is an average of four hours of sunshine a day over the entire year.[59] Snow cover in winter can reach an average of 50 days a year on the highest peaks.[59] Strong winds are an important factor in peat erosion on the summits.[58]

Red deer, once native to Wicklow but hunted to extinction, were reintroduced on the Powerscourt Estate in the 18th century.[69] Japanese sika deer were also imported by the Powerscourt Estate and have interbred with the red deer.[69] All deer found in the Wicklow Mountains are descended from the Powerscourt herd and are either sika deer or hybrid red-sika deer.[70] Other mammals occurring include feral goats, mountain hares, badgers, stoats, otters, red squirrels, grey squirrels and bats.[71] The Irish Elk is an extinct species of deer that lived in the Wicklow Mountains c. 11,000 years ago, remains of which were discovered in great quantities in Ballybetagh Bog near Glencullen.[72]Wolves were also once native to the mountains but were hunted to extinction in Ireland: the last wolf in Wicklow was killed at Glendalough in 1710.[73]

Widespread clearance of forest began in the Bronze Age and continued up until the early 20th century.[74]Afforestation programmes began in the 1920s and accelerated in the 1950s with the widespread planting of conifer forest, especially in upland moorland areas previously considered unsuitable for planting.[75] The dominant tree is the sitka spruce, accounting for 58% of forest plantations,[76] with lodgepole pine, Norway spruce, Scots pine, larch and Douglas fir also planted.[77]Biodiversity is low in the conifer plantations because they are not native tree species.[78]Broadleaf plantations are rare, accounting for less than 10% of forest.[79]

The young rivers in the upper glens are spawning grounds for salmon and brown trout.[80]Arctic char, isolated in the Wicklow lakes following the end of the last ice age,[81] have been recorded in Lough Dan and the lakes of Glendalough but are now believed extinct.[80] A programme to reintroduce them into the Upper Lake at Glendalough commenced in 2009.[82]

The earliest evidence of human activity in the interior of Wicklow dates to around 4,300 BCE.[83]Passage tombs, from the Neolithic period, are the earliest and most prominent feature of prehistoric Irish civilisation in the Wicklow Mountains.[84] These tombs sit on many of the western and northern summits between Saggart in Dublin and Baltinglass in Wicklow, such as at Seefin and Seefingan.[85] Archaeologist Geraldine Stout has suggested they had a territorial marking function, much like modern-day border posts.[86] Other prehistoric monuments to be found in the uplands include stone circles, standing stones and rock art.[87] The presence of standing stones at altitudes suggests they may have served route-marking purposes.[88] The largest complex of hill forts in Ireland is to be found on the hills near Baltinglass.[88]

The earliest known tribes to have controlled the Wicklow Mountains include the Dál Messin Corb, the Uí Mail, the Uí Theig and the Uí Briúin.[89] One member of the Dál Messin Corb was Saint Kevin, who founded the monastery at Glendalough in the latter part of the 6th century.[89] Kevin travelled to Glendalough from Hollywood, crossing the mountains via the Wicklow Gap.[90] By the 8th century, Glendalough had grown into a substantial settlement of 500–1,000 people and an important site of learning and pilgrimage.[91] Monasteries were often attacked, especially at times of disease or famine, and Glendalough's wealth made it a frequent target for both local tribes and, later, Norse invaders.[92] The monastery declined in importance after the arrival of the Normans in the 12th century and its subsequent annexation to the Archdiocese of Dublin.[93] It was burned by the English in 1398, although settlement there continued until the end of the 16th century.[93] There are also important early Irish church sites in the Dublin foothills of the Wicklow Mountains at Rathmichael and Tully.[94]

In 1170, during the Norman invasion of Ireland, Strongbow and Dermot MacMurrough successfully laid siege to Dublin by following a high route through the Wicklow Mountains, avoiding the defences along the normal route to the west of the mountains.[95] The Norman invasion displaced two important Gaelicclans from Kildare, the O'Byrnes and the O'Tooles, who moved into the Wicklow Mountains, the O'Byrnes in the east and the O'Tooles in the west.[96] From their mountain strongholds both families conducted a persistent campaign of harassment against the invaders and the Wicklow Mountains became known as the terra guerre (“land of war”), as opposed to the terra pacis (“land of peace”) of the settled lowlands.[97]

The valley of Glenmalure provided an almost unassailable refuge for the clans and English forces suffered heavy defeats there, first in 1274 and again in 1580 in the Battle of Glenmalure.[98][99] The latter defeat was at the hands of Fiach McHugh O'Byrne, who led many attacks against the English and assisted in the escapes of many of the hostages held by the English to guarantee the loyalty of the Irish clans.[100] One such hostage was Red Hugh O'Donnell, who escaped from Dublin Castle on the night of 6 January 1592 in the company of Art O'Neill.[99] The two men crossed the mountains in blizzard conditions, making for Fiach McHugh O'Byrne's stronghold at Glenmalure.[99] Art O'Neill died from exposure during the journey and Red Hugh had several toes amputated due to frostbite.[101] A cross and a plaque to the north of Conavalla mountain mark the place where Art O'Neill perished and an annual walk is now held following in the two men's footsteps.[102] The O'Byrnes' and O'Tooles' dominance finally came to an end with the Act of Succession of 1652 when their land was confiscated by the English Commonwealth.[103]

Glendalough Valley, showing the Monastic City, the Lower Lake and the Upper Lake

A prolonged period of peace reigned in the Wicklow Mountains from the end of the Cromwellian period until the 1798 Rising.[104] Although the main rebellion was quickly defeated, Irish rebels once again used the Wicklow Mountains as a hiding place and stronghold to attack the English for many years afterwards.[105] Among their number was Michael Dwyer, a native of the Wicklow Mountains, born in the townland of Camara in the Glen of Imaal, and General Joseph Holt.[106] Both men eventually surrendered and were transported to Australia.[106] Determined to prevent any future rebel activity, a military road through the mountains, similar to those built in the Scottish Highlands to quell the Jacobite risings, was proposed by the British government to enable troops to be deployed quickly into the region.[107] The Wicklow Military Road was constructed between 1800 and 1809 and runs from Rathfarnham, County Dublin to Aghavannagh, County Wicklow via Glencree, the Sally Gap and Laragh.[108] A series of army barracks and police stations were built along the route, although they were little used and soon fell into disrepair as the Wicklow Mountains soon ceased to be a centre of rebel activity after the road was completed.[108]

The census of 1841 recorded a population of 13,000 in the Wicklow uplands out of 126,143 persons in the county as a whole.[109] Following the Great Famine, the census of 1891 showed that the population of County Wicklow had declined to 62,136 with the proportionate fall in the uplands regions even greater as the populace deserted the marginal lands.[110]

The construction of the railways in the 19th century led to the development of tourism in the Wicklow Mountains.[111] Visitors were taken by horse-drawn transport into the mountains from the railway station at Rathdrum.[111] Glendalough quickly established itself as the most popular tourist destination and a train service there was considered in 1897 but the proposals came to nothing.[112] The tourism potential of the Military Road was spotted soon after its completion and G. N. Wright's Tours in Ireland (1822) is one of the earliest guides to the sights along the route.[113]

The Dublin foothills of the Wicklow Mountains are managed by the Dublin Mountains Partnership (DMP), a group established in May 2008 with the aim of improving the recreational experience of users of the Dublin Mountains.[124] Its members include representatives of state agencies, local authorities and recreational users.[124] The DMP has restored paths and developed walking trails, orienteering courses and a mountain biking course.[125]